JPS59102896A - Method for controlling shape of single crystal - Google Patents

Abstract

PURPOSE:To carry out the control of the shape of a single crystal in high accuracy, by using a differentiated circuit detecting the weight of pulled single crystal and differentiating the weight signal with time, an operation circuit to carry out the arithmetic operation of the differentiated value, an integrated circuit to integrate the operated value with time, and a deviation detecting circuit to detect the deviation of the integrated value and the differentiated value, and feeding back the deviation to the electrical power for heating. CONSTITUTION:The weight of the pulled single crystal 5 is detected by the weight detector 7, and the signal is sent to the differentiated circuit 8, which differentiates the signal with time and transmits the differentiated result to the operation circuit 9. The operation circuit 9 calculates the value d<2>w/dt<2> from the differentiated value dw/dt according to the formula. The calculated value is integrated with time by the integrated circuit 10, and the integrated value is transferred to the deviation detecting circuit 11. The deviation between the integrated value and the differentiated value is calculated by the deviation detecting circuit 11, and is inputted to the controller 12 to obtain the signal for controlling the electrical power for the heating of crucible. The control signal is inputted to the thermostat 13 to control the heating apparatus 14. The signs A and B in the formula are constants determined by the densities of crystal and molten liquid, etc., and O is prescribed angle of the shoulder part of the single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method for controlling a single crystal into a predetermined shape using the Czochralski method.

[Prior art and its problems]

In the production of single crystals using the Czochralski method, in order to obtain a good single crystal, it is necessary that the diameter of the body of the crystal be constant, and that the shoulders of the crystal have the desired shape. . In particular, controlling the shape of crystal shoulders is an important issue in order to prevent the generation and propagation of strain, dislocations, and twins.

In particular, many reports have been made regarding the relationship between the shape of the shoulder, particularly the angle of layer formation, and the occurrence of twin crystals in single crystals of group 1-V compound semiconductors having a zincblende structure. For example, W,
A, Honner: Mat, Res, l3ul I
, 15<1980), 63.

Since the amount of change in the crystal weight at the shoulder is not constant and changes over time, conventional methods for controlling the shape of a single crystal using a gravimetric method have been carried out as follows. For example, when manufacturing a single crystal with the shape shown in Figure 1a,
The weight change consists of a curved part and a straight part as shown in the graph of Figure 1. This curved part is a cubic function of time,
The straight line part is a linear function of time. Therefore, a reference weight signal can be obtained by directly moving the sliding resistance along a plate with a shape corresponding to this reference weight, or a programmer can move the sliding resistance along a plate with a shape corresponding to the time differential value of the reference weight. −
The reference weight signal was obtained by rotating the motor and moving the heliome (see Japanese Patent Publication No. 4345/1983). Another method has been to use a computer to calculate the time differential value of the reference weight at the shoulder as a linear function of time, and process it using software. This method has been described, for example, by A, E, Zinnes, etal: J
, Cryst.

Growth 19 (1973) 187. It is described in.

□□□□-■□11□□-Li1□- In each of these methods, the reference signal was determined as a function of time and was applied to the oxide single crystal.

By the way, when actually manufacturing single crystals.

In seeding, the shoulder does not always grow in the same way after starting pulling; for example, in seeding, if the temperature is high or low, the crystals may not thicken or thicken rapidly even after pulling. There is a time. Therefore, when controlling the shape of a single crystal using the conventional method, there is a problem in that a large offset tends to occur. If the control is strengthened in order to eliminate this offset, there will be local unevenness at the shoulders, making it impossible to obtain a smooth crystal, resulting in disadvantages such as increased strain and generation of twins. On the other hand, if this offset is left, there is a drawback that the deviation from the predetermined shape is large and the accuracy is poor. This effect is particularly large for Kawa-■ group single crystals.
Conventional shape control methods have not been able to stably grow high-quality ■-■ group single crystal shoulders with good reproducibility. Therefore, in recent years, large-diameter, large-capacity InSb devices have been attracting attention as infrared CCUs, ultrahigh-speed ICs, and FETs.
, GaAs.

There is a drawback that it cannot be applied to the production of ■-■ group single crystals such as InP.

[Purpose of the invention]

This invention was made in view of the above points.

The object of the present invention is to provide a method that eliminates the above-mentioned drawbacks when producing single crystals and can stably produce high-quality single crystals controlled to a predetermined shape with good reproducibility.

[Summary of the invention]

The present inventors believed that the drawback of the above control method is that the reference signal is uniquely determined as a function of time, and that it is necessary to determine it according to the actual growth state of the single crystal.

The time derivative of the weight of a crystal growing with a diameter of 2r (dw
/dt) is expressed by the following formula.

dw/dt=πρ? u=rrp r”H/(1-ρ, γ
p1. R2)・・・・・・(1)S
S Here, ρ and ρ are the densities of the crystal and melt, respectively, Ht is the pulling rate, R is the radius of the crucible, and υ is the crystal growth rate. When formula (1) is differentiated with respect to time and rearranged, formula (2) is obtained.

dtw/dt2=dw/dt (2/r-dr/dt+
1/u・dυ/d t )−(2) This equation shows that the two-time differential value of the crystal weight (d'w/dt") is d w/d t
It is shown that this is expressed by the rate of change in crystal diameter and the rate of change in growth rate. +l) with the linear spread angle at the shoulder as θ
When we sought the relationship between “w/dt” and dw/dt, we found that
It has been found that the following equation (3) can be well approximated except for a portion with a very small diameter.

♂w/dt"=(A-dw/dt+B)θ...
・・・・・・・・・・・・・・・(3) Here, A and B are p
It is a constant determined from s, pt, II, and 几. That is, it has been found that equation (3) is an equation that gives the rate of change of the set value that should be taken next in order to keep the shoulder formation angle constant from the current diameter. From this, dw/dt during pulling
By measuring and integrating d"w/dt" determined from equation (3), it is possible to automatically determine the reference dw/dt according to the actual growth state of the single crystal regardless of time. can. When the shoulder shape of the crystal was controlled using this reference signal, it was found that the offset had a significant effect in improving the grain precision. Therefore, the single crystal shape control method of the present invention includes a differentiating circuit that detects the weight of the pulled single crystal and differentiates the weight signal of the single crystal with respect to time, and a differential value dw/dt that is the output of the differentiating circuit.
From this, we have four operating circuits that calculate based on formula (3), an integrating circuit that time-integrates the calculated value d''w/dt! that is the output of the calculating circuit, and an integral value that is the output of the integrating circuit. The present invention is characterized in that it includes a deviation detection circuit for determining the deviation of the differential value, and controls the shape of the single crystal by feedback-controlling the deviation to the heating power.

〔Effect of the invention〕

As explained above, according to the shape control method of the present invention, (1) extremely accurate layer shape control can be performed stably with good reproducibility in the shoulder growth of a single crystal.

(2) Compared to conventional control methods, changes in crystal growth conditions can be tracked better, so the offset from the predetermined shape is reduced to approximately 115, and the deviation from the linear spread angle at the shoulder is ±1 Can be within °.

(3) In particular, when applied to Ill-V group single crystals, almost no twinning was observed at the shoulders, and a high crystal production yield of 70% or more was obtained.

(4) According to the present invention, single crystals in a predetermined shape can be produced completely automatically, and high-quality crystals can be obtained, so that productivity can be improved by industrial application.

There are other effects.

[Embodiments of the invention]

An embodiment of the present invention will be described in more detail below with reference to the drawings. FIG. 2 is an example of a single crystal manufacturing apparatus equipped with the functions according to the present invention. In the figure, 1 is a container, 2 is a heater, 3 is a crucible, 4 is a melt, 5 is a crystal, 6 is a pulling shaft,
7 is a weight detector, 8 is a differential circuit, 9 is an arithmetic circuit, 10 is an integral circuit, 11 is a deviation detection circuit, 12 is a controller, 13 is a temperature controller, and 14 is a heating device. The weight of the crystal 5 which is being pulled up from the melt 4 in the crucible 3 is measured by a detector 7 and differentiated by a differentiating circuit 8. This signal is input to the next arithmetic circuit 9 to calculate the rate of change of the reference signal. Next, the integration circuit 10 performs integration and automatically sets the reference signal. This reference value and the output of the differentiation circuit 8 are input to a deviation detection circuit 11 to obtain a deviation signal. This deviation signal is input to the adjustment type 12 to obtain a crucible heating power control signal. This control signal is input to the temperature controller 13 to drive the heating device 14,
The shape is controlled by controlling the heating power. The functions of the present invention, from the differentiation circuit 8 to the deviation detection circuit 11, can be configured as shown in FIG. 3, for example.

In the figure, R1 to R14 are resistors, C1 to C2 are capacitors, VRI to VB2 are variable resistors, OP1 to OF2 are operational amplifiers, El is a fixed battery, and 81 is a switch.

OPI is a differentiator circuit 8, OF2 to op4 are arithmetic circuits 9,
OF2 and OF2 constitute an integrating circuit 1O1 and OP7 constitute a deviation detection circuit 11. Here, VRl to VB2 are used to adjust the arithmetic circuit 9 so that it has the input/output characteristics determined by equation (3). Sl is for stopping the operation of the integrating circuit 10 and keeping the output constant, and is used when transferring control from the shoulder to the torso.

Next, as a specific example, a case in which an In8b single crystal, which is a l-V group single crystal, is manufactured using a single crystal manufacturing apparatus having the functions of the present invention will be described in detail. In Fig. 2, 50% of InSb polycrystalline raw material is placed in crucible 3 with a diameter of 75+wm.
0g was added and melted by heating to ~650°C. Next (211
) The seed crystal on the shaft was brought into contact with the melt 4 while rotating at 1° rpm, and then pulling was started at a speed of 10 m/h. At this time, the values of constants A and B in equation (3) are respectively A
=4.77X10/minsdeg, B=6.
It became 65×10 g/minedeg. Therefore, the shoulder formation angle θ was set to 15° and control of the shape of the shoulder was started. When the predetermined diameter was 35 fi, the switch S1 was opened to fix the output of the integrating circuit 10, and the body was continuously pulled up to obtain an InSb single crystal weighing ~450 g. The linear spread angle of the shoulder of the obtained single crystal is ~1
The angle was 4.5°, and the crystal surface was smooth and the crystal was of good quality without twins.

When InSb single crystal was manufactured 10 times in succession using the above control method, the angle deviation of the shoulder part was all ±1.
8 of them were good quality single crystals without twins.

As another embodiment of the present invention, a series of functions of the present invention were implemented in software using a computer as shown in FIG. In the figure, 15 is an AD converter, 16 is a computer, and 17 is a DA converter.

As explained above, according to the method of the present invention, the shape of a single crystal can be controlled with extremely high precision, so that a high quality single crystal can be manufactured with a high yield.

Furthermore, although not described in this embodiment, the shape of the tail of the single crystal can also be automatically controlled in the same way. The method of the present invention can also be applied to other nt-v group single crystals.

For example, GaAs, Garb, Ink-, GaP, etc.
The method can be similarly applied to oxide single crystals by determining the constants A and B in equation (3) depending on the pulling conditions, and the effect obtained is also large.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the relationship between the shape of a single crystal and the crystal weight, and FIG. 2 is a diagram for explaining an embodiment of the present invention.
FIG. 3 is a diagram for explaining one configuration example of the functions of the present invention,
FIG. 4 is a diagram for explaining another embodiment of the present invention. 1... Container, 2... Heater, 3... Crucible,
4... Melt, 5... Crystal, 6... Pulling shaft, 7...
...Weight detector. 8...Differential circuit, 9...Arithmetic circuit, 10...Integrator circuit. 11... Deviation detection circuit, 12... Adjustable type, 13...
- Temperature controller, 14... Heating device, 15... AD converter, 16... Computer, 17... DA converter. Agent: Patent Attorney Noriyuki Chika (and 1 other person) No.
2 Figure 8 Figure 4 Procedure Amendment (Method) 1. Display of the case Patent Application No. 208481 of 1988 2 Title of the invention Method for controlling the shape of single crystals 3 Person making the amendment Relationship to the case Patent applicant (307) Tokyo Shibaura Electric Co., Ltd. 4 Agent address 100 Tokyo 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Miyako March 29, 1981 (shipment date) Engraving of detailed statement (no changes to the contents)

Claims (1)

[Claims] A method for manufacturing a single crystal in which the weight of a single crystal pulled by the Czochralski method is detected and the shape of the single crystal is controlled, comprising: a differentiating circuit for differentiating a weight signal of the single crystal with respect to time; , an arithmetic circuit that calculates the differential value dw/dt, which is the output of the differentiating circuit, based on the following relational expression; an integrating circuit that integrates the calculated value dw/dt'', which is the output of the arithmetic circuit, over time; A shape of a single crystal characterized by comprising a deviation detection circuit for determining a deviation between an integral value that is an output of the integrating circuit and the differential value, and controlling the shape of the single crystal by feedback control of the deviation to heating power. Control method: d!w/dt = (A-dw/dt+ts)・
θ However, A and B are the density of the crystal and melt, the pulling speed is
θ is a preset shoulder forming angle determined from the radius of the crucible.